My experience after testing both Rootly and Incident.io
We spent a few weeks evaluating both incident.io and Rootly after leaving PD. They are close but there's a couple differences. We got good deals from both of them and both helped us leave pagerduty pretty easily so kudos to both companies.
Incident.io has a good UI and the Slack feels pretty polished out of the box. We use Slack a lot and it worked pretty easily and intuitively, pretty easy to get started. Onboarding in general was pretty easy.
The alert routing is clean, the status pages are decent, and the postmortem templates are good enough to get a team to end up writing them. On the con side we found customization not that great. Modeling our process was a bit though and some things were just impossible to translate into incident.io.
We found Rootly interesting. Onboarding was about as smooth as incident.io, and the workflow engine is pretty flexible, we didn't end up running into any walls modeling our incident process. The automation and integrations felt a bit more polished, and there was more room to do things. We also found the postmortems to be a bit better. We felt like it was built a bit more with the capacity to grow with us a company, things like compliance, audits, and more advanced workflows were available without hitting a paywall, which factored into our thinking.
imo neither is perfect or a magic fix and I feel like both have their use cases. That said they do offer far more in terms of capabilities and features than a lot of legacy tools, so I think I'd end up recommending both. We ended up with Rootly because we found it flexible from the start and felt like it would scale better as our needs grew, but again I think both are good tools at what they do, and worth considering at the very least.
edit: small typo